Re: [Qemu-devel] [PATCH v2 1/2] net: introduce MAC_TABLE_CHANGED event

[Michael S. Tsirkin]

On Thu, May 23, 2013 at 01:26:33PM -0400, Luiz Capitulino wrote:
> On Thu, 23 May 2013 20:18:34 +0300
> "Michael S. Tsirkin" <address@hidden> wrote:
> 
> > On Thu, May 23, 2013 at 11:54:03AM -0400, Luiz Capitulino wrote:
> > > On Thu, 16 May 2013 18:17:23 +0300
> > > "Michael S. Tsirkin" <address@hidden> wrote:
> > > 
> > > > > The
> > > > > existing throttling approach ensures that if the event includes latest
> > > > > guest information, then the host doesn't even have to do do a query, 
> > > > > and
> > > > > is guaranteed that reacting to the final event will always see the 
> > > > > most
> > > > > recent request.  But most importantly, if the existing throttling 
> > > > > works,
> > > > > why do we have to invent a one-off approach for this event instead of
> > > > > reusing existing code?
> > > 
> > > Sorry to restart this week old discussion, but I'm now reviewing the patch
> > > in question and I dislike how we're coupling the event and the query
> > > command.
> > > 
> > > > Because of the 1st issue above. A large delay because we
> > > 
> > > Has this been measured? How long is this large delay?
> > > 
> > > Also, is it impossible for management to issue query-rx-filter
> > > on a reasonable rate that would also cause the same problems?
> > > IOW, how can we be sure we're fixing anything without trying it
> > > on a real use-case scenario?
> > 
> > Play with priorities, you can make management arbitrarily slow.  It's
> > just not sane to assume any timing guarantees for tasks running on
> > Linux.
> 
> Would you mind to elaborate? I'm not sure I understand how this answers
> my questions.

Maybe I don't understand the questions.
You are asking why doesn't usual throttling sufficient?
This was discussed in this thread already.
That's because it would introduce a huge delay if guest
changes the mac too often. People don't except that
changing a mac is a thing the should do slowly.

Event throttling was not designed for events where
guest asks management to do something.

-- 
MST